1. Field of Invention
The present invention relates to an etchant, and more particularly, to an etchant for etching a glass substrate uniformly and smoothly.
2. Discussion of the Related Art
As a display device, such as for a television and a personal computer, a large size cathode ray tube(CRT) display device has been used. However, since the screen must be separated from the electron gun by more than a predetermined distance for a large size screen CRT, the volume is increased. Thus, such CRT cannot be applied to a low weight, small size, and low power consumption electronic device such as a wall-mountable television, a portable television, and a notebook computer.
For a small and light display device, a flat panel display devices such as LCD(liquid crystal display), PDP(Plasma display panel), ELD(electroluminescent display), and VFD(vacuum fluorescent display) have been introduced recently. Among the above flat panel display devices, the LCD has been dominantly researched for good picture quality and low power consumption. The LCD-applied portable television and notebook computer have recently been on the market, but there are also problems to be solved in such LCD-applied devices. Particularly, size and weight are important factors to be considered for the LCD.
For small size and light LCDs, there are several methods for reducing the size and weight of the LCD element. However, the driving circuit and the thin film transistor, which are necessary elements of the LCD, are so thin that reducing these elements will not affect the weight in any significant manner. On the other hand, it is possible to reduce the weight of the glass substrate which is a basic element of the LCD. Specifically, since the glass substrate is a heavy element of the LCD, the method of reducing the weight of the glass substrate has been continuously researched.
A light glass substrate means a thin glass substrate. However, thinning of glass substrate causes damage and surface roughness. Thus, the mechanical strength is weakened and the image quality of LCD is deteriorated.
FIG. 1 is a view showing a general method of etching the glass substrate. As shown in FIG. 1, a container 1 is filled with etchant 2 formed of distilled water containing HF. The glass substrates 3 are set within the container 1 in series. The etchant 2 etches the glass substrates 3. However, in this method, when the surface of the glass substrate 3 is etched by the etchant 2, the non-dissolved residue particles are again attached to the surfaces of the glass substrates 3. As a result, the etchant 2 cannot etch the residue particles attached to the substrates 3. Therefore, the glass substrate 3 is not etched uniformly and its surface becomes rough. This non-uniformity of the surface causes a deterioration in image quality of the LCD.
In addition, since the thickness of the glass substrate 3 is not uniform, it can be easily damaged from pressure during use of the LCD.
FIG. 2 is a view showing another etching method of the glass substrate. The feature of this method is that the bubbles 5 are generated by a porous plate 4 within the etchant formed of distilled water containing HF. Not shown in FIG. 2, a gas supplying tube connected to a gas tank is mounted outside of the container 1 to supply the gas to the container 1. The bubbles 5 are supplied to the container 1 through the porous plate 4.
As the bubbles 5 rise up, they separate the non-dissolved residue particles from the surface of the glass substrate 3, so that the total area of the surface of the glass substrate 3 is uniformly etched.
In this method, however, the force of the bubbles 5 exerting on the residue particles attached to the surface of the glass substrate 3 is very weak. Thus, the residue that is tightly attached onto the surface cannot be removed in a practical sense. In addition, since the residue particles separated from the glass substrate 3 are not dissolved in the etchant 2, the etchant causes the pollution which must be filtered.